Medical situations such as the treatment of respiratory problems as well as a wide range of other medical conditions frequently require the delivery of a therapeutic gas(es), such as supplemental oxygen, to a patient or the monitoring of a patient's breathing or exhaled gases, or any combination thereof. The delivery of gases to a patient and the monitoring of a patient's breathing are commonly performed through cannulas, which are typically assemblies of tubes positioned adjacent a patient's nasal passages to deliver gas(es) to or sense breathing via the nostrils.
A cannula for delivering a therapeutic gas to a patient or capturing samples of exhaled breath from a patient, or both, is positioned horizontally between and adjacent to the patient's nose and typically includes an elongated body having an internal gas passage within the cannula body. A cannula typically includes at least one and often two hollow nares that extend upward from the cannula body and the internal gas passage therein and into corresponding ones of the patient's nasal passages to form gas flow paths between the patient's respiratory system, the gas passage within the cannula body and one or more gas delivery and/or sampling lines connected to the body of the cannula and the gas passage therein. In addition, the internal gas passage in the hollow body of a cannula may be divided into first and second halves by an internal septum or partition wall extending across the internal gas passage, thereby dividing the internal gas passage into two, separate gas flow paths and allowing, for example, samples of exhaled breath to be captured on one side of the cannula while permitting a treatment gas to be provided to the patient via the other side of the cannula.
There are essentially two primary methods or systems for delivering a therapeutic gas, such as oxygen, to a patient one of which is referred to as a continuous or constant flow system and the other of which is commonly referred to as an on-demand system. A continuous flow system simply provides a continuous flow of gas to the patient through either or both nares of a cannula. A continuous flow system is thereby relatively simple in operation, needing only a single nare to deliver the gas to the patient and requiring only that the flow of gas be monitored so as to ensure that a flow of gas, at the desired flow volume, continues to flow to the cannula, while the use of multiple nares to deliver the gas reduces the possibility that the flow of gas will be completely interrupted by blockage of any one of the nares. The relative simplicity and possibly lower associated equipment costs of a continuous flow system tend to be offset, however, by the significant costs of providing a continuous flow of gas, including during those portions of the patient's breathing cycle when the patient is not inhaling. Much of the gas is thereby exhausted directly into the surrounding environment and thus wasted.
An on-demand system delivers gas to the patient only during the inhalation portion of the patient's breathing cycle by sensing pressure changes via the cannula, during the patient's breathing cycle, and initiating a timed release or bolus of gas to the patient such that the gas is delivered to the patient at the start of and during the next inhalation breath of the patient's breathing cycle. An on-demand system thereby requires at least one pressure sensing connection to the cannula, e.g., to a nare, in order to monitor and sense pressure changes during the patient's breathing cycle, and one or more gas delivery connections to in the cannula, again to a nare for delivering the gas to the patient.
Examples of “on demand” systems include U.S. Pat. No. 4,462,398 and U.S. Pat. No. 4,519,387 to Durkan et al. wherein a control circuit, responsive to a sensor, operates a valve to supply pulses of respirating gas through a single hose cannula to a respiratory system of a patient when a negative pressure, indicative of the initial stage of inhalation or inspiration, is sensed by the sensor. The pulse of gas delivered to the respiratory system can have a preselected pulse profile. This method provides for supplying a fixed volume of supplemental respiratory gas per unit of time. The volumetric flow rate of the supplemental respiratory gas is preset and the time duration of each application of the supplemental respiratory gas is also preselected, thereby providing a fixed volume of respiratory gas after the beginning of inhalation. Also, this method provides for a minimal delay interval between successive applications of respiratory gas and such delay interval is also predetermined since the time interval for respiratory gas flow is preset for a time less than the time of the inspiration.
Another prior art supplemental oxygen delivery system designed to conserve respiratory gas by delivering oxygen “on demand” only during inhalation is described in U.S. Pat. No. 4,612,928 to Tiep et al. which discloses both a method and apparatus for supplying a gas to a body. The apparatus and method are employed to minimize the amount of oxygen needed to maintain a specific oxygen concentration level in the blood of an individual. The apparatus includes a transducer and other circuit components to obtain a first series of pulses or signals corresponding to the individual's breath rate. A divider or counter processes the signals or pulses of the first series to create a second series of pulses or signals corresponding to periodic pulses or signals of the first series. The pulses or signals of the second series are used to periodically open a valve to deliver oxygen to the individual at about the start of the inhalation interval of the individual's periodic breathing cycles.
Further examples of the prior art, such as U.S. Pat. Nos. 4,457,303 and 4,484,578, recognize that oxygen delivered at the end of the inhalation interval of the breathing cycle is wasteful. These two patents describe respirator apparatuses and methods therefor. In brief, a fluidically-operated respirator comprises an apneic event circuit and a demand gas circuit. The apneic event circuit comprises a variable capacitance device and an exhaust means which rapidly discharges fluid from the circuit when inhalation occurs. The demand gas circuit of the respirator supplies the respirating gas to a patient at the beginning of inhalation and for a time period which is a fraction of the duration of the inhalation. Thus, these patents also follow the reasoning that insufflation at the beginning of inhalation will effectively supply the respirating gas to the patient.
In yet another prior art system, described in U.S. Pat. No. 4,686,974 to Sato et al., a supplemental oxygen delivery system begins to deliver a steady flow of oxygen during a later stage of the exhalation interval and through an advanced stage of the inhalation interval of the breathing cycle and superimposes upon this steady flow of oxygen a peak pulse flow of oxygen at the beginning of inhalation. This device includes a gas source, a valve, an insufflating device, a sensor, and an operational controller. The valve is connected to the gas source so as to regulate flow rate and duration of the gas flow from the gas source. The insufflating device is connected to the valve so as to insufflate the gas therefrom toward a respiratory system of a living body. The sensor is exposed to respiration of the living body and produces electric signals which must distinctively indicate an inhalation interval and an exhalation interval of the breathing cycle. The operational controller receives the electric signals from the sensor and produces control signals to the valve so that gas insufflation starts before the beginning of the inhalation interval and ends before termination of the inhalation interval while providing a short pulse-like peak flow of a large amount of the gas in an early stage of the inspiratory interval. Specifically, steady insufflation of the gas starts before the beginning of each inhalation and the pulse-like peak flow insufflation of the gas is superimposed on the steady insufflation for a short period of time after the beginning of the inhalation. An arbitrary time interval, based upon an average exhalation period and an average inhalation period, is chosen to trigger and end insufflation during the breathing cycle.
Although the prior art devices discussed hereinabove indeed conserve delivery of a treatment gas, such as oxygen, they generally fail to address the problem related to the changing respiratory needs of the patient that vary with different patient activity levels. When a patient requiring supplemental oxygen is at rest, relatively small quantities of oxygen, are required in order to maintain appropriate levels of oxygen concentration in the blood and thereby prevent what is commonly termed “desaturation”. With an increase in the physical activity of a patient, generally larger quantities of oxygen are required in order to maintain appropriate levels of oxygen concentration in the blood of the patient compared to when the patient is at rest.
Such systems are generally referred to as “on the go” systems and an example of such is U.S. Pat. No. 4,706,664 wherein Snook et al. discloses a pulse-flow supplemental oxygen apparatus which yields savings in oxygen while affording the patient the physiological equivalent of a prescribed continuous stream of oxygen. The apparatus includes a demand oxygen valve operated in a pulse mode by electronic control circuitry. Through an appropriate sensor, the electronic control circuitry monitors the patient's breathing efforts and gives a variable timed pulse of oxygen to increase the volume delivered to the patient during the very initial stage of each inhalation interval of the breathing cycle or breath. Pulse volume variability is based upon a measured parameter characterizing a plurality of the patient's preceding breathing cycles. The elapsed time interval of the patient's three preceding breathing cycles is measured to effectively measure the rate of the breathing cycles. These breath-characterizing parameters, together with data characterizing the prescribed continuous oxygen flow to be matched, enable the apparatus to give the desired dose variability.
In yet another example, U.S. Pat. No. 4,584,996 to Blum reveals a method and apparatus for intermittent administration of supplemental oxygen to patients with chronic lung dysfunction. The apparatus is programmable for administering the specific oxygen requirements of the patient and is responsive to changes in these oxygen requirements with increased patient activity. The patient's arterial blood oxygen level is measured while supplying oxygen to the patient during inspiration to determine the number of breathing cycles required to reach a first higher arterial blood oxygen level and is again measured without supplemental oxygen to determine the number of breathing cycles required to diminish the arterial blood oxygen level to a second, lower level. These two cycle numbers are utilized in an algorithm which is applied as a program to the apparatus having a breathing cycle sensor, a counter and control valve. The control valve provides a regulated flow of supplemental oxygen to a nasal cannula for a predetermined number of “ON” breathing cycles and to shut off the flow for a preset number of “OFF” breathing cycles sequentially and repetitively, thereby conserving oxygen while medically monitoring the patient's blood oxygen levels. The oxygen conservation features of this apparatus are further enhanced by turning off the oxygen flow during the exhalation interval of each breathing cycle throughout the “ON” breathing cycles. As the respiratory rate of the patient increases with patient activity, the duration of the “ON” and “OFF” periods changes accordingly.
In U.S. Pat. No. 4,686,975, Naimon et al. teaches a supplemental respiratory device that uses electronic components to intermittently regulate the flow of a respirable gas to a user on a demand basis. By monitoring small changes in the relative airway pressure, this respiratory device supplies gas only when an inhalation is detected. This respiratory device can also vary the duration of the gas delivery time to compensate for changes in the user's breath rate, thereby attempting to adjust for changes in the patient's respiratory needs based upon activity.
U.S. Pat. No. 5,099,836, issued to Rowland et al. on Mar. 31, 1992, relates to a cannula body which supports a pair of spaced apart nares. Each one of the nares has a dividing wall which separates each one of the nares of the cannula into two completely separate flow outlets. A first half of each nare, due to the dividing wall, communicates with the internal flow chamber of the main body of the cannula while a second half of each nare does not communicate with the internal flow chamber but instead communicates, via a side port provide in the side wall of each nare, with a sensing device. The internal flow chamber of the main body of the cannula is connected to a gas supply source, via a first set of tubes, while the sensing device is coupled to the nares of the cannula, by a second set of separate tubes. The dividing wall, within the flares, extends all the way to the inlet/outlet of each nare so that neither one of the nares has a common flow region within the nare and adjacent the inlet/outlet of each nare. As a result of such design, the cannula according to this patent is generally not a divided cannula, that has two internal flow chambers, and is generally cumbersome to utilize due to the additional set of tubes as well as its overall complexity.
A number of other “on demand” and “on the go” systems and cannulas are currently available in the market and Salter Labs, the assignee, of the above identified application, is one supplier of such products.
There are many other examples of “on demand” and “on the go” systems as many manufacturers are marketing oxygen conserver devices which are adapted to retrofit onto typical supplemental oxygen delivery systems that employ any type of oxygen source, such as portable oxygen tanks, oxygen concentrators or wall outlet supplies often utilized in hospitals. These oxygen conserver devices are adapted to be interposed between the oxygen source and a conventional nasal cannula apparatus. Medisonic U.S.A., Inc. of Clarence, N.Y., manufactures an oxygen conserver device entitled MedisO2 nic Conserver. It conserves oxygen by interrupting the flow of oxygen from the source to the patient during the exhalation interval of the patient's breathing cycle. Chad Therapeutics, Inc. of Chatsworth, Calif., manufacturers an oxygen conserver device bearing a registered trademark, Oxymatic® Electronic Oxygen Conserver. Chad's oxygen conserver eliminates oxygen waste during both the exhalation interval and the later portion of the inhalation interval of the breathing cycle. TriTec, Inc. of Columbia, Md., manufactures a demand oxygen cannula for portable oxygen systems that also responds to the negative pressure of inhalation. Smith-Perry Corporation of Surrey, British Columbia, Canada, manufactures The VIC (Voyager Intermittent Controller) Breathsaver that senses every breath of the patient and delivers a measured dose of oxygen only when the patient inhales. Pulsair, Inc. of Fort Pierce, Fla., manufactures an oxygen management system that delivers oxygen to the patient “on demand” at the initiation of inhalation. The Henry G. Dietz Co., Inc. of Long Island City, N.Y., manufactures an oxygen conserver device entitled Hala'tus 1 which conserves oxygen by sensing when inhalation takes places and delivers the oxygen only during inhalation.
While an on-demand or on the go system thereby offers significant reduced costs in terms of gas delivered, in return for increased system complexity and costs, a recurring problem in on-demand systems is the risk that one or more nares may become blocked due, for example, to nasal or respiratory discharges. That is, an on-demand or on the go system employs the cannula nares as the pressure sensing and gas delivery passages.
Conventional cannulas of the prior art, when used for on-demand and on the go systems, however, include only two nares, one of which is used to sense changes in pressure during the patient's breathing cycle to thereby detect the exhalation portion of the breathing cycle and the other of which is used to deliver gas to the patient. If the pressure sensing nare become blocked or occluded for some reason, therefore, the system will cease delivery of gas to the patient because the exhalation portion of the respiratory cycle cannot be detected, so that the delivery of gas cannot be triggered. If, on the other hand, the gas delivery nare becomes blocked, the gas cannot be delivered to the patient even if the gas delivery cycle is suitably triggered.
Lastly, it must be noted that the above described problems with cannulas of the prior art are not confined solely to on-demand gas delivery systems for oxygen and other gases that are triggered by sensing pressure changes during a patient's respiratory cycle. Such problems may appear, for example, in any system requiring the concurrent use of two or more separate passages of the cannula, such as the sensing of a parameter of a patient's respiratory cycle or other medical condition and the concurrent delivery of gas to the patient. Such systems may include, for example, a system for the delivery of oxygen dependent upon the patient's sensed exhaled CO2 levels or a system that monitors the breathing of a patient while concurrently delivering therapeutic gas to a patient independently of the patient's breathing cycle or medical condition, such as a system for monitoring sleep apnea. Others of such systems may include, for example, systems delivering multiple gases and requiring multiple gas delivery paths or systems monitoring multiple aspects of a patient's breathing cycle or medical condition and requiring multiple monitoring paths, or both.
The present invention provides a solution to these as well as other related problems of the prior art.